1. Field of the Invention
The present invention relates to an apparatus for the suppression of the flow noise caused by a throttle valve provided in an intake passage or exhaust passage of an internal combustion engine.
2. Description of the Related Art
In recent years, steps have been taken to prevent the generation of noise from parts of automobiles with a high noise level with the objective of increasing the quietness of the passenger compartment of the automobiles. As the effects of these steps have taken hold, relatively low level noise, which had not been considered a problem in the past, has begun to be treated as problematic. One type of noise audible in the passenger compartment is the noise generated when a throttle valve is opened. This consists of the high frequency flow noise generated from the intake system when the throttle valve provided in the intake passage is made to rapidly open from the fully closed state. This noise is particularly noticeable in recent engines with intake manifolds fabricated out of plastic.
Similar flow noise is generated in the exhaust system of a vehicle having a throttle valve in the exhaust passage as well when causing the throttle valve to rapidly open. This noise also is particularly noticeable in recent engines with exhaust manifolds fabricated from pressed sheet metal. Accordingly, development of a means for suppressing the flow noise generated along with the operation of these throttle valve is becoming urgently required.
One related art being experimented with as a means of suppressing flow noise is illustrated in FIG. 1 and FIG. 2. This was disclosed in Japanese Unexamined Utility Model Publication (Kokai) No. 57-107838 and was aimed at the prevention of backfires. In this art, a metal net 4 was stretched across an air passage 2 inside a throttle body 1 at the downstream side of an ordinary throttle valve 3 provided so as to open and close the air passage 2 (arrow mark shows direction of flow of air). The object of this is to use the metal net 4 to suppress fluctuations in pressure at the downstream side of the throttle valve 3 and thereby try to prevent the generation of noise. This measure, however, has the problem of reducing the engine output somewhat due to the pressure loss of the flow of air.
As another related art, consideration may be given to the method of attaching a noise suppressing cover 5 at the outside of the throttle valve 1 or intake manifold to seal the noise inside the noise suppressing cover. This method is effective in preventing the diffusion of flow noise, but not only is the cost higher, but the weight increases as well. Further, the throttle body 1 and the intake manifold etc. connected to the same become bulkier. Accordingly, there is the disadvantage that a large amount of space is required by the intake manifold etc. in the small engine compartment.
Note that as a means appearing at first glance to be similar to the means of solution of the present invention explained in detail later, there are the two- or more multiple-layer configurations of the intake passages of intake apparatuses of the engines disclosed in Japanese Unexamined Patent Publication (Kokai) No. 62-288318 and Japanese Unexamined Patent Publication (Kokai) No. 1-318756, but the multiple-layer configuration portions of these intake passages are at the upstream sides of the throttle valves. Not only is there a clear difference in configuration from the present invention, but also completely different actions and effects can be expected to be exhibited from the present invention. Further, in the structure of the intake pipe disclosed in Japanese Unexamined Utility Model Publication (Kokai) No. 2-119963, an intake deflection member was provided at the downstream side of the throttle valve, but this constitutes the inflow port of the exhaust gas flowing into the intake pipe for exhaust gas recirculation (EGR) and has a completely different object and different configuration, action, and effect from the present invention.